Phytopathology (2004) 94, 351-363

C.S. Schmidt, F. Agostini, C. Leifert, K. Killham and C.E. Mullins (2004)
Influence of soil temperature and matric potential on sugar beet seedling colonization and suppression of Pythium damping-off by the antagonistic bacteria Pseudomonas fluorescens and Bacillus subtilis
Phytopathology 94 (4), 351-363
Abstract: Pseudomonas fluorescens B5 and Bacillus subtilis MBI 600 colonized sugar beet seedlings at matric potentials of -7 × 10³, -140 × 10³ , and -330 × 10³ Pa and under five temperature regimes ranging from 7 to 35°C, with diurnal fluctuations of 5 to 22°C. No interaction between matric potential and temperature was observed. In situ bioluminescence indicated physiological activity of Pseudomonas fluorescens B5. Colonization of the root at >4 cm below the seed decreased at very low matric potential (-330 × 10³ Pa). Total population size of Pseudomonas fluorescens B5 per seedling was significantly increased at -140 × 10³ Pa. However, matric potential had no significant effect on the population density of Pseudomonas fluorescens per gram of root fresh weight and did not affect the distribution of the population down the root. Total population size per seedling and downward colonization by Pseudomonas fluorescens B5 were significantly reduced at high temperatures (25 to 35°C). Maximum colonization down the root occurred at intermediate temperature (15°C) at both matric potentials (-7 × 10³ and -140 × 10³ Pa). Addition of B. subtilis MBI 600 to the seed had no effect on rhizosphere populations of Pseudomonas fluorescens B5. Populations of B. subtilis MBI 600, which consisted largely of spores, were slightly reduced at lower matric potentials and were not affected by temperature. Survival and dry weight of plants in soils infested with Pythium spp. decreased with increasing soil temperature and matric potential, indicating an increase in disease pressure. However, there was no significant interaction between the two factors. At -330 × 10³ Pa, soil dryness but not Pythium infection was the limiting factor for plant emergence. At temperatures of 7 to 25°C and matric potentials of -7 × 10³ to -120 × 10³ Pa, treatment with Pseudomonas fluorescens B5 increased plant survival and dry weight. At 7°C and -120 × 10³ Pa, there was almost complete emergence of seeds treated with Pseudomonas fluorescens B5. Antagonistic activity of Pseudomonas fluorescens B5 decreased with increasing soil temperature and decreasing matric potential. At 25 to 35°C and -7 × 10³ Pa, no effect was observed. In regimes with different day and night temperatures, the maximum (day) temperature was decisive for disease development and antagonistic activity. B. subtilis MBI 600 displayed no significant antagonistic effect against Pythium ultimum and did not influence the performance of Pseudomonas fluorescens B5 in combined inocula.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Full text of article
Database assignments for author(s): Christoph Stephan Schmidt, Carlo Leifert

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
population dynamics/epizootiology
environment/habitat manipulation

---

Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Globisporangium ultimum	Beet/sugarbeet (Beta vulgaris)
Pseudomonas fluorescens (antagonist)	Globisporangium ultimum	Beet/sugarbeet (Beta vulgaris)
Bacillus subtilis (antagonist)	Globisporangium ultimum	Beet/sugarbeet (Beta vulgaris)